The field of this invention relates to a method of using a diagnostic antigen preparation derived from pseudorabies (PR) virus. More specifically, the invention relates to the use of a diagnostic preparation, which is complementary to the antigen of a PR vaccine, thereby permitting PR virus carriers to be distinguished from vaccinated swine. For convenience of reference, the abbreviation "PR" is used herein to mean "pseudorabies."
Heretofore a diagnostic preparation for determining swine infection by PR virus has been prepared by solubilizing PR virus-infected cells with an aqueous solution of a nonionic detergent. This preparation contains all of the antigens of the virus. When used in a standard test procedure for the presence of serum antibodies to PR virus, such as the enzyme-linked immunosorbant assay (ELISA), swine found positive are assumed to be actual or potential carriers of the virus. However, positive reaction may be due to natural infection and recovery, or to vaccine immunization with whole killed virus, and the swine may not be carriers of the virus. A negative result, however, does permit the determination that the swine are noncarriers.
Sub-unit vaccines for pseudorabies have been developed and shown to be effective. These vaccines are prepared to contain less than the full complement of antigens from the virus, and, specifically, only the glycoprotein antigens of the virus. One method for preparing such a sub-unit vaccine is described in U.S. Pat. No. 4,470,967, entitled "Lectin-Containing Anti-Viral Vaccines for Domestic Animals and Method of Preparation." Example 1 of the cited patent relates specifically to a vaccine of this kind for pseudorabies.
A sub-unit vaccine for pseudorabies containing similar glycoprotein antigens can also be prepared by the method described in U.S. Pat. No. 4,493,825, entitled "Purified and Antigenically Selective Vaccines for Domestic Animals." Particular reference may be had to Examples I and II of the last-cited patent. But it should be understood that the disclosures of these patents are cited only by way of background, and that the details of preparing such subunit lectin-binding glycoprotein vaccines for pseudorabies are not an essential part of the disclosure of the present invention. However, it is one of the important advantages of the diagnostic antigenic preparation of this invention that it can be used as a complementary antigenic preparation with respect to the sub-unit vaccines of the above-cited patents, or of other sub-unit vaccines which are based on lectin-binding glycoproteins of PR virus.
In a prior publication, I have disclosed studies of the pseudorabies virus antigens. Platt, K. B., Vet. Micro. 7 (1982), 515-534. Pseudorabies virus, also known as Aujeszky's disease virus, was solubilized with an aqueous solution of a nonionic detergent. The full complement of antigens was studied and partially characterized, the antigens being divided into Groups I, II and III (see page 521). In separate experiments of the same study, the antigens which were adsorbed on a lectin-agarose gel column (the lectin retentate antigens) were studied. It was found that these were antigens of Group III (see page 524).
Erickson and Kaplan have studied protein synthesis of PR virus. Virology 5 (1973) 94-102. They reported that a protein produced by the PR virus was found in the culture medium and identified this protein by the designation "3a". In the procedure described (page 96, FIG. 2), the cells were infected with the PR virus, the medium was changed at four hours, the cells were then incubated with fresh medium for four more hours, and at eight hours post-infection the culture fluid was electrophoresed with detection of the 3a protein fraction. The 3a protein was found to be sulfated, and was tentatively classified as a mucopolysaccharide or protoglycan.
Erickson and Kaplan did not determine the degree of purity of the 3a protein, or whether the fraction identified was free from viral glycoproteins. Pennington and McCrae subsequently reported that PR virus will elaborate protein which is sulphated and glycosylated. J. Gen. Virol. (1977), 34:155-165. As described by these researchers, the polypeptide 89K is glycosolated very soon after synthesis of the polypeptide chain, and is then sulfated, reduced in size, and excreted. Pennington and McCrae classified protein 89K (assumed to be similar to Erickson and Kaplan protein 3a) as a glycoprotein. They reported that "significant amounts of non-glycosylated precursors were never observed in the medium." (Pennington et al., cited above, page 163.)